Six months out ..Roll Call with the 12 most vulnerable House and Senate seats…

With the House GOP on defense in a difficult national environment, the 10 most vulnerable incumbents six months out from Election Day are all Republicans.

Republicans have pickup opportunities in November, but this is a ranking of the incumbents most likely to lose, not of seats most likely to flip — so there are no open seats on the list.

The biggest change from when we last compiled the list, a year out from Election Day? The most vulnerable member, California Rep. Darrell Issa, is retiring, sliding Iowa Rep. Rod Blum into the top spot. Blum was near the top of the list for most of 2016 — and then he won. But both Republicans and Democrats agree he’s in trouble this year.

Some familiar names shifted around. New York Rep. John J. Faso Jr. slid from third to fifth, while Minnesota Rep. Jason Lewis fell from second to fourth. New York Rep. Claudia Tenney moved up from seventh to sixth.

As always, this list is compiled after consultation with strategists from both sides of the aisle and the race ratings from Inside Elections with Nathan L. Gonzales…..

Senate Democrats are still defending 10 states that President Donald Trump won in 2016, but six months out from Election Day, the most vulnerable senator remains a Republican.

Nevada Sen. Dean Heller no longer faces a primary threat, but he’s the only Republican up for re-election in a state Hillary Clinton won, and in this national environment that’s a tricky place to be.

The Democrats’ odds of flipping a few GOP-held open seats in Arizona and Tennessee have increased over the past six months, but this list — like the one we did a year out from Election Day — ranks incumbents most likely to lose — not seats most likely to flip. That means nine of the 10 senators are Democrats, with the second and third spots remaining unchanged.

North Dakota Sen. Heidi Heitkamp and West Virginia Sen. Joe Manchin III have traded places, with Heitkamp now at fourth and Manchin at fifth. Democrats would have been happy to face Don Blankenship in the West Virginia Senate race, but they’re also not getting Rep. Evan Jenkins, whom they spent nearly $2 million against in the primary.

The biggest change is Florida Sen. Bill Nelson moving up from eighth to sixth with Gov. Rick Scott’s entry into the race. That pushes Montana Sen. Jon Tester and Ohio Sen. Sherrod Brown down a spot each to seventh and eighth, respectively.

As always, this list is compiled after consultation with strategists from both sides of the aisle and the race ratings from Inside Elections with Nathan L. Gonzales…..